Provided is a disc-type ironless permanent magnet synchronous generator powered by an auxiliary power supply, which comprises a stator coil disc and a pair of permanent magnet rotor discs (1) positioned on two sides of the stator coil disc and arranged with a gap therebetween, a circle of main coils (3) are fixedly arranged on the stator coil disc around a center of the disc, the main coil is a main winding of an electric motor to output electric energy, an auxiliary winding independent from the main winding is arranged on a circumference formed by the main coils (3) in a surrounding manner, and output power of the auxiliary winding is less than output power of the main winding.